1. Field of the Invention
The present invention relates to a nanocarbon film, an electrode using the same and a method of production thereof.
2. Description of the Related Art
In recent years, image displays typical in liquid crystal displays (LCDs), plasma displays (PDPs) and electroluminescence (EL) devices have come to be widely used in various fields such as for televisions, computers and various kinds of mobile devices, which have recently become ubiquitous, and there have been remarkable developments therein. Furthermore, due to increased functionality of solar batteries, there have been demands for increased use thereof as way of reducing the use of fossil energy for environmental reasons.
An electroconductive film is used in display devices and solar batteries such as this. An electroconductive film that uses a metallic material including for instance ITO (indium tin oxide) electroconductive films is generally formed by depositing a metallic material on a glass substrate by use of a vapor phase method such as a vacuum deposition method or a sputtering method.
Furthermore, in display devices such as mobile phones and mobile devices, weight reduction by the gram is forwarded; accordingly, a substrate for a display device is demanded to shift from glass to plastics. When a plastic substrate is introduced, a weight of a display device may be reduced to one half or less of that of a device in which a glass substrate is used and the mechanical strength and impact resistance as well are remarkably improved.
However, when a plastic substrate is substituted for a glass substrate, in the case of forming an ITO electroconductive film thereon, the electroconductive film is liable to exfoliate since its adhesiveness is smaller. In addition to what was mentioned above, a film made of a metallic material such as ITO is usually formed by use of a vapor phase method such as a sputtering method; accordingly, a production unit costs much.
It has been proposed to use nanocarbon such as carbon nanotube as an electroconductive material in place of the metallic material. The nanocarbon is a material capable of forming a thin film having electroconductivity by application and has the likelihood of forming the film at low cost.
As a method of producing carbon nanotubes, various kinds of methods such as an arc discharge method, a laser ablation method and a CVD method are known. However, when these methods are used, carbon impurities such as graphite particles and amorphous carbon may become mixed therewith. As a refining method of the carbon nanotubes, for instance, a method in which UV rays are irradiated to remove carbon impurities has been disclosed (Japanese Patent Application Laid-Open (JP-A) 2004-345918).
When carbon nanotubes are used to form a thin film, the carbon nanotubes are difficult to disperse in a medium such as water. Accordingly, a method has been proposed in which a carbon nanotube dispersion is prepared by adding for instance a dispersant and the dispersion is coated on a substrate to form a thin film (WO2004/060798).